diff --git a/cpp/src/db/id_generators.cpp b/cpp/src/db/id_generators.cpp
index 8296a4048f..3541048413 100644
--- a/cpp/src/db/id_generators.cpp
+++ b/cpp/src/db/id_generators.cpp
@@ -1,32 +1,37 @@
 #include <chrono>
 #include <assert.h>
 
-#inlcude "id_generators.h"
+#include "id_generators.h"
 
-using std::chrono;
 
-namespace vecengine {
+namespace zilliz {
+namespace vecwise {
+namespace engine {
 
 IDGenerator::~IDGenerator() {}
 
 IDNumber SimpleIDGenerator::getNextIDNumber() {
-    auto now = chrono::system_clock::now();
-    auto micros = duration_cast<chrono::microseconds>(now.time_since_epoch()).count();
-    return micros * MAX_IDS_PER_MICRO
+    auto now = std::chrono::system_clock::now();
+    auto micros = std::chrono::duration_cast<std::chrono::microseconds>(
+            now.time_since_epoch()).count();
+    return micros * MAX_IDS_PER_MICRO;
 }
 
 IDNumbers&& SimpleIDGenerator::getNextIDNumbers(size_t n) {
     assert(n < MAX_IDS_PER_MICRO);
-    auto now = chrono::system_clock::now();
-    auto micros = duration_cast<chrono::microseconds>(now.time_since_epoch()).count();
+    auto now = std::chrono::system_clock::now();
+    auto micros = std::chrono::duration_cast<std::chrono::microseconds>(
+            now.time_since_epoch()).count();
     micros *= MAX_IDS_PER_MICRO;
 
     IDNumbers ids = IDNumbers(n);
     for (int pos=0; pos<n; ++pos) {
         ids[pos] = micros + pos;
     }
-    return ids;
+    return std::move(ids);
 }
 
 
-} // namespace vecengine
+} // namespace engine
+} // namespace vecwise
+} // namespace zilliz
diff --git a/cpp/src/db/id_generators.h b/cpp/src/db/id_generators.h
index 02f3915bcc..6f24bf36e2 100644
--- a/cpp/src/db/id_generators.h
+++ b/cpp/src/db/id_generators.h
@@ -1,5 +1,4 @@
-#ifndef UTILS_ID_GENERATORS_H_
-#define UTILS_ID_GENERATORS_H_
+#pragma once
 
 #include <vector>
 #include "types.h"
@@ -24,7 +23,7 @@ public:
     virtual IDNumbers&& getNextIDNumbers(size_t n_) override;
 
 private:
-    const MAX_IDS_PER_MICRO = 1000;
+    const size_t MAX_IDS_PER_MICRO = 1000;
 
 }; // SimpleIDGenerator
 
@@ -32,5 +31,3 @@ private:
 } // namespace engine
 } // namespace vecwise
 } // namespace zilliz
-
-#endif // UTILS_ID_GENERATORS_H_
diff --git a/cpp/src/db/types.h b/cpp/src/db/types.h
index 185fb73641..7fd33a0787 100644
--- a/cpp/src/db/types.h
+++ b/cpp/src/db/types.h
@@ -1,5 +1,4 @@
-#ifndef VECENGINE_TYPES_H_
-#define VECENGINE_TYPES_H_
+#pragma once
 
 #include <vector>
 
@@ -7,13 +6,11 @@ namespace zilliz {
 namespace vecwise {
 namespace engine {
 
-#define uint64_t IDNumber;
-#define IDNumber* IDNumberPtr;
-#define std::vector<IDNumber> IDNumbers;
+typedef uint64_t IDNumber;
+typedef IDNumber* IDNumberPtr;
+typedef std::vector<IDNumber> IDNumbers;
 
 
 } // namespace engine
 } // namespace vecwise
 } // namespace zilliz
-
-#endif // VECENGINE_TYPES_H_